Microfiber knot laser operates evanescently

A fiber-ring laser developed by researchers at Zhejiang University (Hangzhou, China) and Fudan University (Shanghai, China) consists of a silica microfiber tied into a knot.

Th 0707lfw Nbf2

A fiber-ring laser developed by researchers at Zhejiang University (Hangzhou, China) and Fudan University (Shanghai, China) consists of a silica microfiber tied into a knot. In an interesting twist, the active medium is the dye solution in which the fiber is immersed; pumped by 532 nm light from within the solid fiber, the dye solution lases between 570 and 580 nm, evenescently coupling its light back into the microfiber knot.

Th 0707lfw Nbf2
Click here to enlarge image

A central section of a standard single-mode fiber is drawn down to a micrometer-diameter microfiber, and then tied into a knot having a diameter of a few hundred micrometers. Pulsed pump light (6 ns pulse duration) is lens-coupled into the fiber and through the taper into the knot structure. The closeness of the 1.43 refractive index of the solution to the 1.46 index of the fiber ensures a large evenescent field that excites the dye, with a lasing threshold of 9.2 µJ/pulse. Three lasing groups (each of many individual wavelength peaks) centered around 567, 570, and 580 nm were observed. Optimizing the evenescent fields, improving the Q factor, and better resonating the pump and signal light together in the knot. Contact Limin Tong at [email protected]

More in Optics